Conventionally, a vehicle headrest device (for example, see Patent Document 1 (pp. 6-8, and FIGS. 1-4)) is known as a technique for adjusting the position of a headrest provided on a seat of a vehicle such as an automobile, etc. When this vehicle headrest device moves the front portion of the headrest in a direction to be fully opened, an ECU of the device judges based on a detection result of a capacitance sensor that the front portion of the headrest has come close to the head of a vehicle occupant and stops the front portion of the headrest.
The ECU judges that the front portion of the headrest has come close to the head of the vehicle occupant based on an absolute capacitance change from a reference capacitance value of the capacitance sensor or based on an amount of change of the capacitance value.
A vehicle occupant protecting device (for example, see Patent Document 2 (pp. 3-6, and FIGS. 1-5)) is a technique for moving a headrest, which is movable forward with respect to the vehicle, to a pre-crash phase before an object crashes into the vehicle from behind. This device controls the amount to move the headrest frontward based on how a capacitance sensed by a capacitance sensor changes.
A vehicle occupant sensing system (for example, see Patent Document 3 (pp. 3-5, and FIGS. 1-4)) generates a weak electric field around a plurality of strip-shaped antenna electrodes which are provided in a horizontal state in a backrest (or a seat back) of a seat with a gap provided therebetween in the vertical direction. The system detects a current flowing through the antenna electrodes based on the weak electric field.
Then, the system extracts the shoulder line of the vehicle occupant sitting on the seat based on the detected current, senses the position of the head based on the shoulder line, and sends data based on the sensing result to an air bag device. In this way, the system sets the air bag of the air bag device to a deployable or non-deployable state.